Hi,
'cache some files' sounds like a EJB specification violation.
You should not access from EJB's any file (see http://www.oracle.com/technetwork/java/javaee/tech/index-jsp-142185.html)
If you want to read something like a configuration you should implement a MBean to read the file and provide the information.
And remember that use of a cache should only be implemented if you have detected a bottleneck and measured that it will help.
In my experience caches where implemented without effect (e.g. not often used) or negative effect (e.g. performance reduced or nasty sideeffects)